:The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

/pdf/soil-carbon-sequestration-impacts-on-global-climate-change-1w7459lbbk.pdf

Soil carbon sequestration impacts on global climate change and food security.

Climate Change 2007 Synthesis report

Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and

/pdf/the-causes-of-land-use-and-land-cover-change-moving-beyond-3nfu1yqkcy.pdf

The causes of land-use and land-cover change: moving beyond the myths

The relationship between soil structure and the ability of soil to stabilize soil organic matter (SOM) is a key element in soil C dynamics that has either been overlooked or treated in a cursory fashion when developing SOM models. The purpose of this paper is to review current knowledge of SOM dynamics within the framework of a newly proposed soil C saturation concept. Initially, we distinguish SOM that is protected against decomposition by various mechanisms from that which is not protected from decomposition. Methods of quantification and characteristics of three SOM pools defined as protected are discussed. Soil organic matter can be: (1) physically stabilized, or protected from decomposition, through microaggregation, or (2) intimate association with silt and clay particles, and (3) can be biochemically stabilized through the formation of recalcitrant SOM compounds. In addition to behavior of each SOM pool, we discuss implications of changes in land management on processes by which SOM compounds undergo protection and release. The characteristics and responses to changes in land use or land management are described for the light fraction (LF) and particulate organic matter (POM). We defined the LF and POM not occluded within microaggregates (53–250 μm sized aggregates as unprotected. Our conclusions are illustrated in a new conceptual SOM model that differs from most SOM models in that the model state variables are measurable SOM pools. We suggest that physicochemical characteristics inherent to soils define the maximum protective capacity of these pools, which limits increases in SOM (i.e. C sequestration) with increased organic residue inputs.

Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

/pdf/climate-change-and-water-2dpc0zbpsj.pdf

Climate change and water.

Eight wheat (Triticum aestivum L.) cultivars including soft white spring, hard red spring, Canada Prairie Spring (CPS) and durum types were grown on rain-fed and irrigated land from 1987 to 1990 at Lethbridge, AB, to assess the relationship between yield components and radiation-use efficiency. Canopy reflectance measurements were used to estimate seasonal absorption of photosynthetically active radiation (APAR). At maturity, yield components including tillers per plant, heads per plant, kernels per head and kernel weight were determined. Whole-plant phytomass and grain yield were also determined. Harvest index was determined from the ratio of grain yield to whole-plant (excluding roots) phytomass and radiation-use efficiency (RUE) was calculated from the ratio of whole-plant phytomass to APAR. Significant grain yield differences confirmed that soft white and CPS wheats yielded more and responded more to irrigation than hard red or durum wheats. The yield components that were consistently different among ...

Morphological characteristics of wheat associated with high productivity

Cereals grown under irrigated conditions in the Canadian prairies produce large amounts of residues and proper management of these residues is required to produce good crop yields and maintain soil quality. Field studies from 1986 to 1990 assessed the effect of straw-tillage treatments on plant growth of irrigated cereals on a Dark Brown Chernozemic Lethbridge (Typic Boroll) loam in southern Alberta. The crop sequence was wheat (Triticum aestivum L.)-wheat-oats (Avena sativa L.) wheat. Straw was retained on the plots or removed by baling. Tillage treatments were autumn mouldboard ploughing, spring mouldboard ploughing or direct seeding.

Grain yield was greater in the autumn plough compared with the spring plough treatments (4336 kg ha−1 vs. 3763 kg ha−1, respectively) in 1 year (1989) out of 4. Grain yield was greater in the no straw-spring plough than the straw-spring plough treatment (4242 kg ha−1 vs. 3791 kg ha−1, respectively) in 2 years out of 4. Spring plough treatments had the advantage of ground cover over winter compared with autumn plough treatments. The problems associated with straw incorporation in the spring could be alleviated by removing the straw by baling but this practice removed 16.0 kg N ha−1 year−1 and 1600 kg C ha−1 year−1 from the soil system. Grain N concentration was decreased by 10% if straw was incorporated in the spring compared with autumn incorporation. Straw N concentration was decreased with spring ploughing compared with autumn ploughing when straw was incorporated and also when straw was removed by bailing. Total plant N was decreased by spring ploughing compared with autumn ploughing if straw was incorporated. Incorporation of straw also decreased total plant N compared with removing the straw with spring but not with autumn ploughing. Under a no straw-direct seeding treatment, grain yield and plant N uptake were generally less than in the no straw-tillage systems.

Straw-tillage treatment effects on grain yield and plant N uptake were attributed to differences in seedbed quality and mineral N levels. Lower spring and autumn soil NO3N levels in the straw-spring plough and direct seeding treatments throughout the 4 crop years were attributed to great N immobilisation compared with the autumn plough and no straw-spring plough treatments.

This field study showed that although spring incorporation of straw and direct seeding treatments encountered seedbed problems and lower N availability, these treatments with added N could be as productive and be more sustainable systems than other treatments as they enjoy advantages in terms of better soil conservation and less harmful environmental impact.

Crop residue management for irrigated cereals on the semi-arid Canadian prairies☆

Managing nitrogen (N) inputs to sustain high yields while minimizing losses to adjacent environments remains among the foremost aims in agroecosystems. We studied the N balance in a study established in 1911 at Lethbridge, AB, Canada. The experiment includes three cropping systems — continuous wheat (W), fallow–wheat–wheat (FWW), and fallow–wheat (FW) — with a factorial of two N rates (0 and 45 kg N ha−1) and two phosphorus (P) rates (0 and 20 kg P ha−1) superimposed beginning in 1967. In unfertilized subplots, grain yields generally increased for the first eight decades, but then declined, perhaps partly because of growing N deficiency. Yield response to N increased over time, especially under continuous cropping and when co-applied with P. Soil N concentration in the surface 15 cm declined in the first few decades, and then approached an apparent steady state. Application of N increased soil N, roughly in proportion to the amount of residue returned. For the first half-century (1911–1967), N removal was...

https://bioone.org/journals/Canadian-Journal-of-Soil-Science/volume-97/issue-4/cjss-2016-0118/Nitrogen-balance-in-century-old-wheat-experiments/10.1139/cjss-2016-0118.pdf

Nitrogen balance in century-old wheat experiments

Smith, E. G., Janzen, H. H. and Krobel, R. 2015. Yield and profitability of fallow and fertilizer inputs in long-term wheat rotation plots at Lethbridge, Alberta. Can. J. Plant Sci. 95: 579–587. A long-term, 42-yr study was used to determine the impacts of crop rotation and fertility management on wheat yield and profitability. Crop rotations included continuous wheat (W), fallow–wheat (FW), and fallow–wheat–wheat (FWW). Original plots were split for nitrogen (N) and phosphorus (P) fertility treatments, a two-factor factorial for N (0 and 45 kg ha−1) and P (0 and 20 kg ha−1). Phosphorus increased yield during the first half of the period, but had little impact during the last half. Nitrogen had no yield impact on fallow crops during the first half of the period, but had a positive impact during the last half, and throughout for wheat after wheat. The soil became incapable of releasing adequate N for wheat after fallow. Simulated distributions of net returns determined the W rotation with N and P fertilize...

https://bioone.org/journals/canadian-journal-of-plant-science/volume-95/issue-3/CJPS-2014-356/Yield-and-profitability-of-fallow-and-fertilizer-inputs-in-long/10.1139/CJPS-2014-356.pdf

H. Henry Janzen

Papers

Morphological characteristics of wheat associated with high productivity

Crop residue management for irrigated cereals on the semi-arid Canadian prairies☆

Nitrogen balance in century-old wheat experiments

Yield and profitability of fallow and fertilizer inputs in long-term wheat rotation plots at Lethbridge, Alberta

Spatial pattern of ammonia sorption by soil and vegetation downwind of a beef feedlot